The present disclosure relates generally to an immersion lithography system used for the manufacture of semiconductor devices, and more particularly to the seal ring carrier of the immersion lithography system.
The manufacture of very large-scale integrated (VLSI) circuits requires the use of many photolithography process steps to define and create specific circuits and components onto the semiconductor wafer (substrate) surface. Conventional photolithography systems comprise of several basic subsystems, a light source, optical transmission elements, photo mask reticles, and electronic controllers. These systems are used to project a specific circuit image, defined by the mask reticles, onto a semiconductor wafer coated with a light sensitive film (photoresist) coating. As VLSI technology advances to higher performance, circuits become geometrically smaller and denser, requiring lithography equipment with lower resolution (smaller feature size) projection and printing capability. Such equipment is now required to be capable of producing features with feature resolutions smaller than 100 nanometers (nm). As new device generations are developed requiring even further improvements, of feature resolutions 65 nm and lower, major advancements to photolithography processing are required.
Immersion lithography has been implemented to take advantage of the process technology's capability for much improved resolution. Immersion lens lithography features the usage of a liquid medium to fill the entire gap between the last objective lens element of the light projection system and the semiconductor wafer (substrate) surface during the light exposure operations of the photoresist pattern printing process. The liquid medium used as the immersion lens provides an improved index of refraction for the exposing light, thus improving the resolution capability of the lithographic system. This is represented by the Rayleigh Resolution formula, R=k1λ/N.A., where R (feature size resolution) is dependant upon k1 (certain process constants), λ (wavelength of the transmitted light) and the N.A. (Numerical Aperture of the light projection system). It is noted that N.A. is also a function of the index of refraction where N.A.=n sin θ. Variable n is the index of refraction of the liquid medium between the objective lens and the wafer substrate, and is θ the acceptance angle of the lens for a transmitted light.
It can be seen that as the index of refraction (n) becomes higher for a fixed acceptance angle, the numerical aperture (N.A.) of the projection system becomes larger thus providing a lower R value, i.e. a higher resolution. Conventional immersion lithographic systems utilize de-ionized water as the immersion fluid between an objective lens and the wafer substrate. At one of the wavelengths, for example 193 nm, de-ionized water at 20 degree Celsius has an index of refraction at approximately 1.44 versus air which has an index of refraction at approximately 1.00. It can be seen that immersion lithographic systems utilizing de-ionized water as the immersion fluid, offers a significant improvement to the resolution of the photolithography processes.
One challenge of utilizing the immersion lithography system is to seal the wafer on a wafer chuck/stage. A seal ring is used for protecting the wafer from fluid turbulence and particulate contamination. However, the seal ring needs frequent cleaning to get rid of the particles. Frequent loading and unloading of the seal ring and/or the wafer demands for an appropriate carrier mechanism to operate with the seal ring.
What is desired is an improved seal ring arrangement for the immersion lithography operations.